An invisible, odorless gas that puts the person inhaling it to sleep in a matter of minutes. When roused the victim will be grumpy, able to open only one eye, and will immediately fall back to sleep.
This gas is given off by turkeys cooking, TVs, car engines, and warm pine trees at a rest stop on a long bicycle ride.

"Uncle Tom is asleep on the couch in front of the TV and we haven't even had the Thanksgiving turkey yet!"
"Yeah, there is a lot of Lethargon gas in the house right now. Look, there goes Uncle Dick too!"